1. Field
This disclosure relates to voltage mirroring circuits supplying scalable voltage biases across all circuits in voltages zones to prevent over-voltage stress at minimum cost in voltage headroom, and more particularly relates to voltage scaled biasing and device stacking for high-voltage operations.
2. Description of the Related Art
In conventional communication systems there is a tradeoff between transmission speed and transmission distance. As lithography and wafer processing technologies enable fabrication of circuits with finer features and thinner gate oxides, the next generation circuits will continue to operate at ever higher speeds, but the over voltage (OV) rating at which these circuits become susceptible to dielectric breakdown also continues to decrease, according to the Johnson limit. Communicating over long distances with large attenuation can require that the transmitted signal is sent as a high voltage signal exceeding the OV rating of fast circuits having thin gate oxides.
For example, a 28 nm thick oxide is rated at 1.8V, and thus a 28 nm thick oxide does not support high voltage, e.g., 3.3V, applications such as Ethernet over unshielded twisted pair (UTP). On the other hand, laterally diffused MOSFET (LDMOS) circuits are compatible with operation at 3.3V across the drain and source. However, LDMOS circuits are too slow and bulky for wideband applications such as 1000BASE-T1 automotive Ethernet.
Some conventional circuits use device stacking to extend the upper bound of voltage scaling in technologies using devices with low OV ratings. However, device stacking also creates inflexibility at the lower bound of voltage scaling, making it difficult to manufacture a single high-bandwidth circuit capable of satisfying alternatively the requirements for low power operation when high voltage signals are not required, and trading off power consumption for high voltage operation when high voltage signals are required. For example, in case of low attenuation and low noise (e.g., in a communication system using short coaxial cables), power saving may be desirable or even mandatory by decreasing the supply voltage. However, the flexibility to decrease the supply voltage may be absent in circuits using conventional device stacking configurations. A wide range of voltage scaling can provide an important advantage, for example, in 100/1000BASE-T1 automotive and small business Ethernet applications. Conventional circuit configuration can be improved to provide better voltage scaling, creating flexibility in a single circuit to alternatively transmit high-voltage signals in applications with high attenuation or noise or by scaling down the supply voltage to save power by transmitting lower voltage signal in applications without high attenuation and noise.